Processes for coloring of thermoplastic polymers are well known. The colorants used for coloring the thermoplastics can be either pigments or dyes. Pigments are organic or inorganic particles that are insoluble in polymers. Dyes are organic liquids that are soluble in the plastic.
A masterbatch is a concentrate of pigments dispersed into a carrier resin. Masterbatches are used to color plastics by adding the masterbatch to the plastic to be colored prior to or during the coloring process. Known masterbatches generally include a colorant, a dispersing agent, a carrier resin, which is typically a thermoplastic polymer, and optionally one or more additives. Masterbatches are often used because they provide better colorant dispersion than neat colorant.
The most commonly used dispersing agents known in the art are metal soaps, such as calcium stearate, zinc stearate, magnesium stearate, aluminium stearate and ethylene bisstearamide (EBS) wax.
It is known that migration problems can arise when dispersing agents are used in the process of coloring thermoplastics. This problem is most likely to occur during coloring of very non-polar plastics, such as for example polyethylene and polypropylene, where the more polar dispersing agents tend to migrate to the surface. Such migration causes problems in form of non-uniform coloring of the plastic.
Known masterbatches have a relatively low colorant concentration, because larger concentrations result in insufficient dispersion of the colorant particles.
Insufficient dispersion of colorant particles can lead to uneven coloring of the polymers and color spots due to non optimal distribution of the pigment particles. Insufficient dispersion of colorant particles can also lead to a decrease in physical and mechanical properties of the end product, such as tensile strength, flexural modulus, elongation and impact strength. Additional problems caused by insufficient dispersion include thread breakage during spinning and clogging filters of melt spinning equipment.
US 2008/0319123 describes a polyester, which contains carboxy groups, for use as a dispersing agent in pigment concentrates for coloring of thermoplastics. The document also describes masterbatches comprising pigments, thermoplastics and said polyester.
U.S. Pat. No. 5,604,279 relates to a colorant preparation, which can be used for producing masterbatches or for the direct coloration of plastics. The colorant composition contains 60-90% by weight of an organic or inorganic pigment, 5-39% by weight of an amorphous poly-alfa-olefin and 0.1-10% by weight of a free-flow agent. The free-flow agent is silica, preferably pyrogenic silica, chalk, a silicate, preferably an aluminium silicate, a sodium silicate, a sodium aluminium silicate or a calcium silicate, or a polyol ester of a long-chain fatty acid, oleamide or a partial fatty acid glyceride.
JP 3274183 discloses a dispersant for a coloring agent. The coloring agent is a mixture of dispersant in a pigment. The dispersant comprises an ester formed from a condensed hydroxy fatty acid having a degree of condensation of at least 2 or greater and a polyhydric alcohol having 4 or more hydroxyl groups as an essential component. The document is not concerned with masterbatches for coloring of thermoplastic polymers, nor does the document discuss the problem of providing an even distribution of colorant pigments in a masterbatch.
EP 0799855 describes a filler-containing thermoplastic resin composition having good flowability and toughness and improved impact strength, bending strength and other mechanical properties and heat stability. The document does not relate to a composition, such as for example a masterbatch, for coloring of thermoplastic polymers.